1. Field of the Invention
This invention relates to a vertical injection molding machine for continuously manufacturing a slide fastener chain by molding a pair of coupling element rows on and along confronting edges of a pair of parallel fastener tapes being conveyed horizontally and also molding top and bottom stops, if necessary. More particularly the invention relates to a vertical injection molding machine, for manufacturing a slide fastener chain, which machine is equipped with a plurality of injection units on a rotary disc situated above upper and lower mold halves so that change of color of molding material and change of molding material can be performed in a short time by rotating the rotary disc, always securing high dimensional precision. In addition the invention relates to a support structure for the rotary disc of the vertical injection molding machine.
2. Description of the Related Art
Generally in the conventional vertical injection molding machines, for example, automatic color change is performed by discharging residual chips off the screw, putting cleaning chips into the screw, cleaning inside the screw, supplying new molding chips to be used for the next molding, and making several empty shots, whereupon normal operation starts. Therefore color changing takes a considerable time (about two minutes) which would influence greatly on the productivity of recent years' flexible manufacturing.
In order to reduce the time for color change, etc., a solution has been proposed by, for example, Japanese Patent Publication No. SHO 63-23892 disclosing a vertical injection molding machine in which a plurality of injection heads are supported on a fixed table so as to be rotatable about a vertical axis and in which a plurality of sets of fixed and movable mold halves are arranged concentrically over upper and lower rotary discs via upper and lower attachment plates, respectively, the upper and lower rotary discs being situated under the fixed table and rotatable about the same vertical axis with respect to the rotational axis of the injection heads.
In this known vertical injection molding machine, the upper mold half near the injection nozzle is the fixed mold half, while the lower mold half remote from the injection nozzle is the movable mold half. At the time of color change, the used injection head is moved to the color changing position, and the other injection head for which arrangements have previously been made for the next injection is moved to the injection position, in an effort to perform the switching of the injection heads within a short time. In this case, since simultaneously with the switching, the sets of movable and fixed mold halves also can be changed, it is possible to form different molded products by replacing the mold sets with desired mold sets one after another.
However, the above-mentioned publication merely discloses a vertical injection molding machine in which the rotary disc rotatable on the fixed table supports the plural heavy-weight injection units and is totally silent about any countermeasure, setting aside a rotating means for the rotary disc, against the excessive load while the rotary disc is rotating. Thus when the excessive load is exerted on the rotary disc, a considerably large drive motor is necessary in smoothly rotating the rotary disc sliding on the fixed table in face-to-face contact.
Using rollers or balls on one of the confronting surfaces of the rotary disc and the fixed table could be considered in an attempt to smoothly rotate the rotary disc on the fixed table while the excessive load is exerted on the rotary disc. But the relationship between the rotary disc and the fixed table is satisfied not only by realizing merely smooth rotation of the rotary disc but also by surely fixing the rotary disc at a predetermined position on the fixed table during the injection molding. Therefore, existence of rollers and balls would make it difficult to position and secure the rotary disc on the fixed table.
Further, in the prior art vertical injection molding machine equipped with plural injection units, the injection cylinder and a number of members to be actuated by liquid pressure, e.g. a lock mechanism to be actuated hydraulically, rotate about the same axis. The number of liquid-pressure pipes to be connected to these many members for actuation is necessarily large; some pipes tend to cross one another or tend to be twisted or bent so that they can easily damaged, thus requiring laborious maintenance.
Furthermore, partly since the injection heads are situated above the fixed table and partly since the plural sets of upper and lower mold halves are situated under the fixed table, the fixed mold half and the movable mold half must be upper and lower ones, respectively, in order to reduce the vertical stroke of the injection nozzle to a minimum.
A slide fastener chain is a continuous length of opposed tapes having opposed coupling element rows on and along confronting edges of the respective tapes; if such slide fastener chain is to be processed (to a correct size) with high precision, it is necessary to control the tension of the slide fastener chain with very high precision while it is being continuously conveyed. But assuming that this prior art vertical injection molding machine is used in molding coupling element rows on a slide fastener chain, it is necessary to convey the slide fastener chain hanging in midair and contacting the cavity surface of the fixed upper mold half. If the chain were guided on the movable lower mold half, it would have been necessary to move a slide fastener chain conveyor upwardly and downwardly in synchronism with the moving of the lower mold half toward and away from the upper mold half, thus making the mechanism complex and larger in size and hence impractical.